This invention is a continuation-in-part-application of U.S. patent application Ser. No. 46,078, filed June 6, 1979, now abandoned and copending U.S. patent application Ser. No. 266,222, filed May 11, 1981 now abandoned.
Mushrooms commonly lose approximately 25% to 30% or more of their fresh weight when subject to the blanching process prior to canning. The blanching process is designed to inactivate certain enzymes and partially sterilize the mushrooms and involves either steam or boiling water cooking for approximately five (5) minutes to bring the internal temperature to 180.degree. F. or above.
Sterilization after canning normally results in an additional 10% to 15% weight loss. Sterilization is normally accomplished in a pressure vessel and involves bringing the temperature at the middle of the sealed can to 250.degree. F. and holding this temperature a sufficient time to destroy thermophylic organisms which may be present and complete the sterilization.
The combination of these two processes result in an expected weight loss during canning of mushrooms of 35% to over 40%.
The extreme weight loss sets mushrooms apart from other vegetables as does the fact that they are a macro fungi rather than a chlorophyl producing plant.
The weight loss that is experienced in the canning process makes the canned product more expensive than fresh mushrooms. The canned mushroom, upon further cooking such as sauteing, still experiences a further weight loss.
Several processes have been proposed for reducing the weight loss experienced during canning mushrooms. U.S. Pat. No. 3,843,810, to Fehmerling proposes applying a vacuum down to lower than 13 mm of mercury in a slow, controlled descent followed by at least one hour at the minimum pressure then a slow increase in pressure to ambient, while soaking the mushrooms in a water solution. The process takes a minimum of two hours in the vacuum and preferably three hours. The average yield after blanching given by Fehmerling with a three hour process is given as 84%. Additionally, Fehmerling shows a series of comparisons between his process and other vacuum processes.
The best previous process known to the present inventors is shown in U.S. Pat. No. 4,143,167, to Blanchaud, et al. This process also uses a vacuum down to approximately 50 mm to 60 mm of mercury in a solution wherein is disolved 1% to 6% dried egg albumin or equivelent. The albumin is then coagulated during the blanching process. This treatment does succeed in reducing the weight loss somewhat, however, the resulting product has objectionable coagulated albumin hanging from it and the texture is noticably tough and rubbery.
Mushrooms, after harvest, are normally commercially stored at approximately 32.degree. F. to retard further respiration which would result in opening of the veil which makes them less desirable and to reduce the weight loss during storage since mushrooms continue to respire after harvest.
It is known to commercial canners and shown in the experiments of McArdle, et al., in 1962, that there is a relationship between the length of post harvest storage and the amount of weight loss experienced during canning. The small reduction of the weight loss is partially offset by the weight loss in storage due to respiration of the mushroom along with deterioration of color and blemishing and the increased number of "opens" or lower grade mushrooms from extended storage. Even this slight reduction in weight loss prompts most mushrooms canneries to store fresh mushrooms at about 32+ for two to three days prior to canning.